Thermostatic expansion valves and methods of control

ABSTRACT

A method of operating a refrigeration system is provided. The method includes activating an evaporator heater ( 306 ), monitoring a pressure differential within the refrigeration system ( 308 ), when the pressure differential reaches a predetermined value ( 310 ), deactivating the evaporator heater ( 312 ), and activating one or more evaporator fans ( 314 ), after deactivating the evaporator heater, to cause a thermostatic expansion valve to open.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Stage of Application No. PCT/US2016/045222,filed on Aug. 3, 2016, which claims the benefit of U.S. ProvisionalPatent Application No. 62/200,242, filed on Aug. 3, 2015, thedisclosures of which are incorporated herein by reference.

BACKGROUND

The subject matter disclosed herein generally relates to thermostaticexpansion valves and, more particularly, to control and operation ofthermostatic expansion valves in refrigeration systems.

In a typical refrigeration system, high pressure liquid refrigerant isexpanded in an expansion valve incorporated in a liquid refrigerant linebetween a condenser and an evaporator. The low pressure, low temperaturerefrigerant discharged from the expansion valve is then directed throughthe evaporator for absorbing heat and thus refrigerating the spacesurrounding the evaporator. The expansion valve is adjusted to controlthe refrigerant flowing into the evaporator to a rate sufficient tomaintain a desired temperature of the evaporator. More specifically, athermostatic expansion valve meters the flow of refrigerant into theevaporator in proportion to the rate of evaporation of the refrigerantin the evaporator, and is responsive to the temperature of therefrigerant leaving the evaporator and to the pressure in theevaporator. In this manner, a thermostatic expansion valve can controlthe refrigerant leaving the evaporator at a predetermined superheat.

Generally, the superheat of the refrigerant is a measure of the heatcontained in the refrigerant vapor above its heat content at the boilingpoint (saturation temperature) at the existing pressure (i.e., the heatcontent of the refrigerant vapor exiting the evaporator coil which is inexcess of the heat content of the vapor which normally could be expectedat the refrigerant pressure as it exits the evaporator). By ensuringthat the condition of the refrigerant entering a suction line from theevaporator (i.e., evaporator outlet) is at a desired superheat level,the performance of the refrigeration system can be efficient and thereturn of liquid to a compressor may be prevented.

A thermostatic expansion valve typically includes a spring-biasedmetering valve which regulates the flow of liquid refrigerant throughthe expansion port to the evaporator. A thermostatic bulb charged with avolatile substance is positioned in heat exchange relation with thesuction line of the refrigeration system at the outlet of theevaporator. The thermostatic bulb is interconnected by means of acapillary tube to a diaphragm actuator included on the thermostaticexpansion valve with the diaphragm actuator being mechanicallyinterconnected to the metering valve of the thermostatic expansionvalve. A rise in the evaporator temperature will increase thetemperature of the evaporated gas passing through the suction line(i.e., increase its superheat) which in turn is sensed by thethermostatic bulb. The thermostatic bulb absorbs heat and the volatilesubstance therein increases its pressure and thus causes the diaphragmactuator to open the metering valve of the expansion valve and to thusproportionately increase the flow of refrigerant. Upon cooling of theevaporator, the temperature of the refrigerant discharged from theevaporator will decrease which in turn is sensed by the thermostaticbulb thereby resulting in the metering valve of the thermostaticexpansion valve to at least partially close and to block at least aportion of the refrigerant flowing to the evaporator.

SUMMARY

According to one embodiment a method of operating a refrigeration systemis provided. The method includes activating an evaporator heater,monitoring a pressure differential within the refrigeration system, whenthe pressure differential reaches a predetermined value, deactivatingthe evaporator heater, and activating one or more evaporator fans, afterdeactivating the evaporator heater, to cause a thermostatic expansionvalve to open.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the pressuredifferential is monitored between an input side and an output side of anevaporator.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the predeterminedvalue is 50 psi.

In addition to one or more of the features described above, or as analternative, further embodiments may include determining that therefrigeration system failed to start prior to activating the evaporatorheater.

In addition to one or more of the features described above, or as analternative, further embodiments may include that determining that therefrigeration system failed to start is based on a detected current drawof a compressor.

In addition to one or more of the features described above, or as analternative, further embodiments may include starting a compressor ofthe refrigeration system after the thermostatic expansion valve is open.

In addition to one or more of the features described above, or as analternative, further embodiments may include, after starting thecompressor, starting a condenser and then starting an evaporator.

In addition to one or more of the features described above, or as analternative, further embodiments may include activating one or morecondenser fans after activating the evaporator heater.

In addition to one or more of the features described above, or as analternative, further embodiments may include, when the pressuredifferential reaches the predetermined value, deactivating the one ormore condenser fans.

In accordance with another embodiment, a refrigeration system includes acompressor, a condenser having one or more condenser fans, an evaporatorhaving an evaporator heater and one or more evaporator fans, athermostatic expansion valve, a fluid path fluidly connecting thecompressor, the condenser, the evaporator, and the thermostaticexpansion valve, and a controller. The controller is configured toactivate the evaporator heater, monitor a pressure differential withinthe fluid path, when the pressure differential reaches a predeterminedvalue, deactivate the evaporator heater, and activate the one or moreevaporator fans to cause the thermostatic expansion valve to open.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller is configured to determine that the compressorfailed to start prior to activating the evaporator heater.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller monitors a current draw of the compressor todetermine the compressor failed to start.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller is configured to perform a start attempt of thecompressor after the thermostatic expansion valve is opened.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller is further configured to, after starting thecompressor, start the condenser and then start the evaporator.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller is configured to activate the one or more condenserfans after activating the evaporator heater.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the controller is configured to, when the pressure differentialreaches the predetermined value, deactivate the one or more condenserfans.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the pressure differential is monitored between an input side and anoutput side of the evaporator.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includethat the predetermined value is 50 psi.

In addition to one or more of the features described above, or as analternative, further embodiments of the refrigeration system may includeat least one sensor configured to sense a pressure differential withinthe fluid path.

According to another embodiment, a method of operating a refrigerationsystem is provided. The method includes determining that therefrigeration system failed to start, increasing a temperature at a bulbof a thermostatic expansion valve system within the refrigerationsystem, increasing a suction pressure at an inlet side of an evaporatorin the refrigeration system, opening a thermostatic expansion valve, andstarting a compressor of the refrigeration system.

In addition to one or more of the features described above, or as analternative, further embodiments may include that increasing thetemperature comprises activating an evaporator heater.

In addition to one or more of the features described above, or as analternative, further embodiments may include that increasing the suctionpressure comprises activating one or more condenser fans.

In addition to one or more of the features described above, or as analternative, further embodiments may include monitoring a pressuredifferential within the refrigeration system and when the pressuredifferential reaches a predetermined value, activating one or moreevaporator fans to cause the thermostatic expansion valve to open.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the pressuredifferential is monitored between an input side and an output side ofthe evaporator.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the predeterminedvalue is 50 psi.

In addition to one or more of the features described above, or as analternative, further embodiments may include that determining that therefrigeration system failed to start is based on a detected current drawof the compressor.

In addition to one or more of the features described above, or as analternative, further embodiments may include, after starting thecompressor, starting a condenser and then starting the evaporator.

Technical effects of embodiments of the present disclosure include anrefrigeration system having a thermostatic expansion valve that may beelectro mechanically manipulated such that the refrigeration system mayeasily be restarted after shut-down.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be understood, however, the following descriptionand drawings are intended to be illustrative and explanatory in natureand non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter is particularly pointed out and distinctly claimed atthe conclusion of the specification. The foregoing and other features,and advantages of the present disclosure are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a schematic illustration of an refrigeration system inaccordance with an example embodiment of the present disclosure;

FIG. 2 is a plot schematic of pressure, temperature, and time of asystem in accordance with an example embodiment of the presentdisclosure; and

FIG. 3 is a process of operating a refrigeration unit in accordance withan example embodiment of the present disclosure.

DETAILED DESCRIPTION

As shown and described herein, various features of the disclosure willbe presented. Various embodiments may have the same or similar featuresand thus the same or similar features may be labeled with the samereference numeral, but preceded by a different first number indicatingthe figure to which the feature is shown. Thus, for example, element “a”that is shown in FIG. X may be labeled “Xa” and a similar feature inFIG. Z may be labeled “Za.” Although similar reference numbers may beused in a generic sense, various embodiments will be described andvarious features may include changes, alterations, modifications, etc.as will be appreciated by those of skill in the art, whether explicitlydescribed or otherwise would be appreciated by those of skill in theart.

FIG. 1 is a schematic illustration of a refrigeration system inaccordance with an example embodiment. The refrigeration system 100includes a compressor 102, a condenser 104, and an evaporator 106 thatare fluidly connected by a flow path 108. Located between the condenser104 and the evaporator 106 is a thermostatic expansion valve assembly110. Flow of a fluid in the flow path 108, such as a coolant orrefrigerant, may be controlled by the thermostatic expansion valveassembly 110. The condenser 104 and the evaporator 106 may include oneor more fans 105, 107, respectively. In some embodiments the fans 107 ofthe evaporator 106 may be high speed fans.

The thermostatic expansion valve assembly 110 includes a valve 112 at aninput side 114 of the evaporator 106 along the flow path 108. Thethermostatic expansion valve assembly 110 also includes a sensor bulb116 at an output side 118 of the evaporator 106 along the flow path 108.The valve 112 meters flow of the fluid to the evaporator 106 based on atemperature of the fluid that has passed through the evaporator 106, assensed by the sensor bulb 116. For example, if the fluid sensed by thesensor bulb 116 is above a predetermined temperature, then the valve 112will be opened to permit fluid to pass through the evaporator 106,thereby cooling the evaporator 106. If the fluid is sensed to be belowthe predetermined temperature, the valve 112 will close to prevent theevaporator 106 from becoming over cooled. Additionally, as shown in FIG.1, an evaporator heater 120 may be thermally connected to the evaporator106 and configured to prevent overcooling of the evaporator 106.

Because of the temperature comparison, and dependency, of thethermostatic expansion valve assembly 110, there may be situations wherethe valve 112 may not open when it is desired to be opened. For example,during use the valve 112 may be closed, in order to prevent overcoolingof the refrigeration system. However, when the refrigeration system 100is shut down after use, the valve 112 may remain closed. When the valveis closed, the pressure in the refrigeration system 100 may not be ableto equalize. Then, when the refrigeration system 100 is attempted to berestarted, due to the high pressure, the compressor 102 may draw a highcurrent to operate. This may cause a safety feature to activate, thuspreventing the refrigeration system 100 from starting.

Those of skill in the art will appreciate that the schematic andconfiguration shown in FIG. 1 is merely an example and other componentsor configurations are possible. For example, refrigeration systems mayinclude controllers 122, receivers, filters, dryers, additional valves,heat exchangers, sensors 124, indicators, etc. without departing fromthe scope of the present disclosure.

Embodiments of the present disclosure are configured to enable startingof a refrigeration system, even when the pressure within the system isunequal across a thermostatic expansion valve assembly. In someembodiments, the evaporator heaters are utilized to raise the saturationtemperature in the evaporator coil above a return air temperature. Then,turning on the evaporator fans after the heat is removed, the saturationpressure is lowered quickly and the thermal bulb temperature of thethermostatic expansion valve assembly remains warm, creating a sensedhigh superheat causing the valve of the thermostatic expansion valveassembly to open. When the valve opens, the discharge pressure islowered by flowing refrigerant back into the evaporator and reducing thedifferential pressure. Thus, the refrigeration system may be startedwithout pulling too much current.

Turning to FIG. 2, a temperature-pressure-time plot is shown. On thisplot, pressure is shown on the left vertical axis, temperature is shownin the right vertical axis, and time progresses from time zero andincreases to the right in FIG. 2. The plot 200 represents a time periodbeginning at T₀ when a compressor of a refrigeration system is attemptedto be started, but fails to start. Such a situation may occur when apressure differential in the system is too high to enable the valve of athermostatic expansion valve assembly to open. In accordance with theshown example in FIG. 2 the process is an example of automaticallystarting the refrigeration system after a failed start. For example, theprocess described with respect to FIG. 2 may be performed on a systemsimilar to that shown in FIG. 1.

In FIG. 2, line 202 represents the discharge pressure or the pressure ofa fluid at the outlet of the evaporator over time (e.g., at output side118 of FIG. 1). For example, this may be the pressure at the bulb. Line204 represents the temperature at the bulb over time (e.g., at bulb 116of FIG. 1). Line 206 represents the suction pressure or the pressure atthe inlet to the evaporator (e.g., at input side 114 of FIG. 1).

As noted above, at T₀ the compressor of a refrigeration system isattempted to be started, but fails to start. Then, at time T₁ theevaporator heat (e.g., evaporator heater 120 of FIG. 1) is turned on.Additionally, at time T₁ the fans of the condenser are turned on. Asshown in FIG. 2, at time T₁ a pressure differential ΔP₁ between thedischarge pressure 202 and the suction pressure 206 is present.

Between time T₁ and time T₂ the suction pressure 206 may increase, thedischarge pressure may decrease slightly and/or plateau and thetemperature at the bulb may significantly increase. The temperatureincrease in the bulb may be a result of the operation of the fans andthe heaters. For example, the heaters may heat the temperature of afluid within the evaporator and the condenser fans may blow or more theheated air through the evaporator and toward the bulb. Accordingly, thesaturation temperature in the evaporator may be raised above the returnair temperature, i.e., at the outlet.

At time T₂ a critical pressure differential is created. For example, attime T₂, a pressure differential ΔP₂ may be present between thedischarge pressure 202 and the suction pressure 206. As shown, thedifferential pressure ΔP₂ is less than the differential pressure ΔP₁ attime T₁. When the differential pressure, e.g. differential pressure ΔP₂,reaches a predetermined pressure differential, the evaporator heater andthe condenser fans are turned off. In some embodiments the predeterminedpressure differential may be 50 psi, although the pressure differentialmay be set at any value depending on the needs of the system. At thesame time, the evaporator fans are turned on. Further, at time T₂, thebulb temperature 204 is much higher than the return air temperature.

After the heater and condenser fans are turned off and the evaporatorfan is turned on, the saturation pressure is lowered quickly while thebulb temperature remains warm. This results in a sensed high superheatthat causes the thermostatic expansion valve to open at time T₂. Theopening lowers the discharge pressure 202, as shown after time T₂, byflowing fluid back into the evaporator and keeping the differentlypressure low (for example, at or below the predetermined differentialpressure ΔP₂). With the thermostatic expansion valve open, thecompressor of the refrigeration system may be started easily at time T₃.

Turning now to FIG. 3, a process 300 in accordance with the presentdisclosure is shown. Process 300 may be similar to the process describedwith respect to FIG. 2 and may be performed with a refrigeration systemsimilar to the shown in FIG. 1 or variations thereof.

The process begins when a compressor is attempted to be started, butfails to start (step 302). As described above, this may occur whenattempting to restart the compressor after shutdown, and the pressuredifferential within the system causes a valve of a thermostaticexpansion valve assembly is closed and cannot be opened. It will beappreciated by those of skill in the art that this situation may arise,for certain systems, during a period after shutdown of the compressor.The period may be, in some examples, twelve hours or less, and in someother systems it may be six hours or less. This time period is a resultof the natural equilibrium that is obtained over time after a shut down.However, if the system is attempted to be activated within this timeperiod, the pressure remaining in the system may prevent the valve fromopening and thus prevent the compressor from starting.

A determination is made that the compressor failed to start (step 304).To determine if the system failed to start, the current drawn by thecompressor may be monitored. If a predetermined current is exceeded bythe draw of the compressor, it may be indicated that an attempt was madebut the compressor failed to start. As such, a current draw at the timeof startup that exceeds a predetermined level may trigger the remainingsteps of process 300.

When it is determined that the compressor failed to start uponinitiation, a thermostatic expansion valve of the refrigeration systemmay be manipulated. For example, to force the thermostatic expansionvalve to open, a heater of an evaporator and fans of a condenser may beturned on (step 306). This process may heat up the temperature near abulb of the thermostatic expansion valve assembly, and may further alterthe pressure differential across the evaporator. As the components ofstep 306 are run, the pressure differential across the evaporator may bemonitored (step 308).

When it is determined that the pressure differential reaches apredetermined value (step 310), the evaporator heater and the condenserfans may be turned off (step 312). In some embodiments, the pressuredifferential may be monitored until a 50 psi differential exists.

Alternatively, at steps 308/310, rather than monitor a pressuredifferential, a predetermined amount of time may elapse. That is, whenthe evaporator heater and condenser fans (step 306) are operated for apredetermined amount of time, the components may automatically shut off(alternative step 312)

At the same time, or shortly after step 312, the evaporator fans may beturned on (step 314). As a result, the bulb of the thermostaticexpansion valve assembly may sense a high superheat which causes thethermostatic expansion valve to open. A starting attempt may be repeated(step 316). If the starting attempt fails (step 316), the process mayreturn to steps 302/304.

After the compressor is started (step 316) additional steps may beperformed as part of process 300. For example, after the compressor isstarted, the condenser may then be activated, and then the evaporatormay be activated. In some embodiments, the staggered or staged start upmay have each component start-up separated by a predetermined amount oftime.

As will be appreciated by those of skill in the art, a controller may beconfigured with a refrigeration system to perform process 300, asdetailed above. That is, in FIG. 1, the refrigeration system 100 mayinclude a processor or other control device, as known in the art, tocontrol the system. The controller may be configured as part of thecompressor 102, part of the condenser 104, and/or part of the evaporator106, or may be separate from the components of the refrigeration system100, but in communication therewith.

Such controller may be in communication with one or more sensors orother devices that may enable the process to be performed. Suchcontroller system is known in the art and is not shown or furtherdescribed herein. However, it will be appreciated that the controllersystem may be configured to perform the steps of process 300 and/orcarry out the process described with respect to FIG. 2, and/orvariations thereof.

Advantageously, embodiments described herein provide a refrigerationsystem that is configured to easily restart after a failed startingattempt. Further, advantageously, embodiments disclosed herein allow foran electromechanical manipulation of the thermostatic expansion valve toequalize system pressure. Further, advantageously, embodiments disclosedherein may reduce the amount of current required to start the compressorafter a failed start attempt. Further, advantageously, embodimentsdisclosed herein may enable equalization of the pressure ratio across acompressor and lower the condenser pressure to give the compressor theopportunity to start under a lighter load.

Further, advantageously, those of skill in the art will appreciate thatthe systems, methods, and processes may be used for other purposes. Forexample, the systems, methods, and processes described herein may beused to improve compressor reliability. For example, the pressure withinthe system, e.g., the delta pressure, may be lowered across compressorfor each start of the compressor, for the life-time of the compressor,or for some other period or other specified start times. As such, theembodiments described herein are not required to be used for failedstarts, but may be used to control the pressure differential within thesystem for any desired purpose.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. Rather, the present disclosure can be modified toincorporate any number of variations, alterations, substitutions,combinations, sub-combinations, or equivalent arrangements notheretofore described, but which are commensurate with the spirit andscope of the present disclosure. Additionally, while various embodimentsof the present disclosure have been described, it is to be understoodthat aspects of the present disclosure may include only some of thedescribed embodiments.

For example, although only one simple configuration of a refrigerationsystem is shown and described, those of skill in the art will appreciatethat other components and/or features may be added to the system withoutdeparting from the scope of the disclosure. Further, configurations ofthe components may be used without departing from the scope of thedisclosure. Moreover, although described in a specific order of stepsand/or timeliness, those of skill in the art will appreciate that theseare merely examples, and the process may be varied depending on theneeds and configurations that employ the process.

Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A method of operating a refrigeration systemcomprising: determining that the refrigeration system failed to startprior to activating an evaporator heater based on a detected currentdraw of a compressor, wherein a failed start is based on a current drawof the compressor exceeding a predetermined current; activating theevaporator heater; monitoring a pressure differential within therefrigeration system; when the pressure differential reaches apredetermined value, deactivating the evaporator heater; activating oneor more evaporator fans, after deactivating the evaporator heater, tocause a thermostatic expansion valve to open; and restarting therefrigeration system.
 2. The method of claim 1, wherein the pressuredifferential is monitored between an input side and an output side of anevaporator.
 3. The method of claim 1, wherein the predetermined value is50 psi.
 4. The method of claim 1, further comprising starting thecompressor of the refrigeration system after the thermostatic expansionvalve is open.
 5. The method of claim 4, further comprising, afterstarting the compressor, starting a condenser and then starting anevaporator.
 6. The method of claim 1, further comprising activating oneor more condenser fans after activating the evaporator heater.
 7. Themethod of claim 6, further comprising, when the pressure differentialreaches the predetermined value, deactivating the one or more condenserfans.
 8. A refrigeration system comprising: a compressor; a condenserhaving one or more condenser fans; an evaporator having an evaporatorheater and one or more evaporator fans; a thermostatic expansion valve;a fluid path fluidly connecting the compressor, the condenser, theevaporator, and the thermostatic expansion valve; and a controllerconfigured to: determine that the refrigeration system failed to startprior to activating the evaporator heater based on a detected currentdraw of the compressor, wherein a failed start is based on a currentdraw of the compressor exceeding a predetermined current; activate theevaporator heater; monitor a pressure differential within the fluidpath; when the pressure differential reaches a predetermined value,deactivate the evaporator heater; activate the one or more evaporatorfans to cause the thermostatic expansion valve to open, and restart therefrigeration system.
 9. The system of claim 8, wherein the controlleris further configured to, after starting the compressor, start thecondenser and then start the evaporator.
 10. The system of claim 8,wherein the controller is configured to activate the one or morecondenser fans after activating the evaporator heater.
 11. The system ofclaim 10, wherein the controller is configured to, when the pressuredifferential reaches the predetermined value, deactivate the one or morecondenser fans.
 12. The system of claim 8, further comprising at leastone sensor configured to sense a pressure differential within the fluidpath.
 13. A method of operating a refrigeration system comprising:determining that the refrigeration system failed to start based on adetected current draw of a compressor, wherein a failed start is basedon a current draw of the compressor exceeding a predetermined current;increasing a temperature at a bulb of a thermostatic expansion valvesystem within the refrigeration system; increasing a suction pressure atan inlet side of an evaporator in the refrigeration system; monitoring apressure differential within the refrigeration system and when thepressure differential reaches a predetermined value, activating one ormore evaporator fans to open a thermostatic expansion valve; restartingthe refrigeration system; and starting the compressor of therefrigeration system.